Methods and apparatuses for communication between a mobile terminal and a base station during a random access procedure

ABSTRACT

The disclosure relates to a method in a mobile terminal for communication with a base station in a wireless network during a random access procedure. The method comprises exchanging ( 202 ) between the mobile station and the base station, during the random access procedure, information on a selected DRX scheme to be used for communication between the mobile terminal and the base station in the random access procedure, setting ( 204 ) the mobile terminal in DRX mode according to the selected DRX scheme and receiving ( 206 ) at least one message from the base station during the random access procedure, wherein the at least one message was transmitted according to the selected DRX scheme. The disclosure also relates to a corresponding method in a base station, and to a mobile terminal and a base station. By such methods, base station and mobile terminals, battery power in a mobile terminal may be saved during a random access procedure.

PRIORITY

This nonprovisional application is a U.S. National Stage Filing under 35U.S.C. §371 of International Patent Application Serial No.PCT/CN2012/070810, filed Apr. 20, 2012 and entitled “Methods andApparatuses for Communication Between a Mobile Terminal and a BaseStation During a Random Access Procedure”.

TECHNICAL FIELD

The present disclosure relates generally to methods and an apparatusesfor communication between a mobile terminal and a base station during arandom access procedure.

BACKGROUND

With an increased number of user equipments (UEs) such as smart phonesin mobile networks, network operators are confronted with a number ofnew challenges. For example, users of smart phones require an experienceof being always on-line, similar to the experience of being connected tothe Internet via a personal computer. This always on-line experiencemeans short reaction time for data arrival and data transmission. Anatural way of solving this would be to let all smart phones in thenetwork be always connected to the network, i.e. for a Long TermEvolution (LTE) network the smart phones would always be in theRRC_Connected state. Although, to let the smart phones be alwaysconnected consumes a lot of network resources and UE battery power.

One reason for high UE power consumption and consumption of networkresources is the network controlled handover procedure for users in theRRC_Connected state. Such handover procedures cause UE random accessprocedure operations and RRC reconfiguration operations which increaseUE power consumption and network signaling costs. This is especiallytrue when there are many smart phones in a cell and many of them aremoving with a high speed (e.g. on a train).

FIGS. 1a and 1b show simulation results for random access channel (RACH)failure and power consumption for mobile terminals travelling in anetwork, wherein the mobile terminals are simulated to have the samevelocity at a simulation, but different velocity between eachsimulation. As could be seen in FIG. 1a , the number of random accessfailures, i.e. the number of times a random access attempt does notsucceed, would largely increase when the number of smart phones in acell increases from around 2000 smart phones/cell when the smart phonestravel at 120 km/h. The random access failures are caused by manysimultaneous random access attempts, at the same time as there are alimited number of preambles dedicated for handover, which leads torandom access channel decoding error and collisions. As could be seen inFIG. 1b , the increase in random access failures is followed by asimilar increase in UE power consumption. This is at least partlybecause a UE consumes lots of power when it is performing a randomaccess procedure and because the random access failure is followed by anew random access attempt until the random access procedure issucceeded.

US2009457653 shows a procedure in which the UE is in sleep mode in a socalled back-off period, which is a period between two consecutive randomaccess procedures that may occur due to a random access failure. Bysetting the UE in sleep mode in the back-off periods, UE powerconsumption at random access procedures is decreased.

Although, there is still a need to decrease the UE power consumption atrandom access procedures.

SUMMARY

It is an object of the invention to address at least some of theproblems and issues outlined above. It is possible to achieve theseobjects and others by using a method and an apparatus as defined in theattached independent claims.

According to one aspect, a method is provided in a mobile terminal forcommunication with a base station in a wireless network during a randomaccess procedure. The method comprises exchanging, between the mobileterminal and the base station, during the random access procedure,information on a selected DRX scheme to be used for communicationbetween the mobile terminal and the base station in the random accessprocedure, setting the mobile terminal in DRX mode according to theselected DRX scheme and receiving at least one message from the basestation during the random access procedure, wherein the at least onemessage was transmitted according to the selected DRX scheme. When themobile terminal is set in DRX mode it is set to be in sleep mode exceptfor in certain time intervals when it is set to wake up and listen tosignals sent from a BS. The DRX scheme defines at which time intervalsthe mobile terminal should be awake and listen to signals from the BS.When the BS and the MT has exchanged DRX scheme, the BS may only sendsignals destined to the MS at the time intervals defined by the DRXscheme. The method in the mobile terminal may further comprise the stepof waking up from a sleep mode at time points or time intervals definedby the DRX scheme to receive messages from the base station during therandom access procedure.

By exchanging information on DRX scheme to be used between the mobileterminal and the base station and by receiving messages from the basestation according to the exchanged DRX scheme during the random accessprocedure, it is possible for the mobile terminal to be in sleep modeduring the random access procedure and only wake up at time intervalswhen the base station may transmit according to the exchanged DRXscheme. Thereby, mobile terminal power may be saved during a randomaccess procedure.

Also, by enabling DRX during a random access procedure, air interfaceresources are saved. Further, by enabling DRX during a random accessprocedure it is possible to prioritize between high and low priorityusers during a random access procedure. For example, low priority usersmay have DRX enabled during a random access procedure, and high priorityusers may monitor continuously during the response window and contentionresolution timer. As another example, low priority user may be set witha DRX scheme with few and short awake periods for the receiver to listento signals and high priority users may be set with a DRX scheme withmore frequent and/or longer awake periods. Examples of low priorityusers are machine type communication or machine to machinecommunication, which are in general delay tolerant. Without applyingembodiments of this disclosure, a scheduler cannot distinguish a lowpriority user from a normal UE and will handle the low priority userequal to the normal UE which affect normal UE performance. And even if ascheduler can distinguish a low priority user from a normal UE, withoutapplying embodiments of this disclosure, both low and high priority userwill have to monitor continuously.

According to another aspect, a method in a base station is provided forcommunication with a mobile terminal in a wireless network during arandom access procedure. The method comprises exchanging, during therandom access procedure, between the mobile station and the basestation, information on a selected DRX scheme to be used forcommunication between the mobile terminal and the base station in therandom access procedure, setting the base station in a DRX modeaccording to the selected DRX scheme, and transmitting at least onemessage to the mobile terminal during the random access procedure,wherein the at least one message is transmitted according to theselected DRX scheme.

According to a third aspect, a mobile terminal is provided forcommunication with a base station in a wireless network during a randomaccess procedure. The mobile terminal is arranged for exchanging, duringthe random access procedure, with the base station, information on aselected DRX scheme to be used for communication between the mobileterminal and the base station in the random access procedure. The mobileterminal further comprises a setting unit for setting the mobileterminal in DRX mode according to the selected DRX scheme, and areceiver for receiving at least one message from the base station duringthe random access procedure, wherein the at least one message wastransmitted according to the selected DRX scheme.

According to a fourth aspect, a base station is provided forcommunication with a mobile terminal in a wireless network during arandom access procedure. The base station is arranged for exchanging,during the random access procedure, with the mobile terminal,information on a selected DRX scheme to be used for communicationbetween the mobile terminal and the base station in the random accessprocedure. The base station further comprises a setting unit for settingthe base station in a DRX mode according to the selected DRX scheme, anda transmitter for transmitting at least one message to the mobileterminal during the random access procedure, wherein the at least onemessage is transmitted according to the selected DRX scheme.

The above methods, mobile stations and base stations may be configuredand implemented according to different optional embodiments. In onepossible embodiment, the information on the selected DRX scheme isexchanged by the base station sending the information of selected DRXscheme to the mobile terminal. I.e. the selection of DRX scheme iscontrolled by the base station. In another embodiment, the informationon the selected DRX scheme is exchanged by the mobile station selectinga preamble which is mapped to a certain DRX scheme, and thereaftersending the preamble to the base station. Since the mapping is known toboth the mobile terminal and the base station, the base station willknow the selected DRX scheme when receiving the preamble. I.e. thisselection of DRX scheme is controlled by the mobile terminal.

Further possible features and benefits of this solution will becomeapparent from the detailed description below.

BRIEF DESCRIPTION OF DRAWINGS

The solution will now be described in more detail by means of exemplaryembodiments and with reference to the accompanying drawings, in which:

FIG. 1a is a diagram showing the relation between system load andaverage number of RACH failures per UE per second for UEs havingdifferent velocities, in a prior art system.

FIG. 1b is a diagram showing the relation between system load andaverage UE power consumption for UEs having different velocities, in aprior art system.

FIG. 2 is a signaling diagram of a random access procedure according toprior art.

FIG. 3 is a signaling diagram of a random access procedure according toa possible embodiment of the invention.

FIG. 4 is a signaling diagram of a random access procedure according toanother possible embodiment of the invention.

FIGS. 5-7 are flow charts of methods in a mobile terminal according topossible embodiments.

FIGS. 8-10 are flow charts of methods in a base station according topossible embodiments.

FIG. 11 is a schematic block diagram of a mobile terminal and a basestation according to possible embodiments.

DETAILED DESCRIPTION

Based on the understanding that power consumption of a UE during arandom access procedure may be a critical issue, especially for e.g.certain traffic cases resulting in many reoccurring random accessprocedures, the inventors have come up with different suggestions of howto enable DRX mode in an ongoing random access procedure.

Briefly described, a solution is provided for decreasing UE powerconsumption during a random access procedure. This is achieved byexchanging information on a DRX scheme to be used between the UE and thebase station in communication with the UE during the random accessprocedure and setting the UE and the base station in DRX mode accordingto the exchanged DRX scheme. Thereafter the base station transmits atleast one message during the random access procedure according to theexchanged DRX scheme. Since the UE and the BS have exchanged informationon DRX scheme, the UE knows the moments in time when the at least onemessage may be transmitted and the UE only needs to wake up to listenfor a message from the base station at the moments in time defined bythe DRX scheme. Thereby, UE power is saved.

A random access procedure may be performed in e.g. the followingsituations: when performing an initial access when there is no RRCconnection with the base station; upon initial access to a target cellwhile the UE is in a handover process; upon request by a command of thebase station; during a correction procedure when there is radio linkfailure or handover failure. A random access procedure can also betriggered to acquire a UL grant or a Timing Advance (TA) command etc.

The full random access procedure according to the current LTE protocol3GPP TS 36.321, E-UTRA, Medium Access Control (MAC) protocolspecification is shown in FIG. 2. According to the protocol, the UE 110selects 2.1 a preamble (contention-based preamble), or use an indicatedpreamble (non contention-based preamble) and sends 2.2 the preamble tothe eNodeB 120. Then the UE actively listens for a random accessresponse message (MSG2) 2.3 from the eNodeB during a response timewindow. During this window the UE consumes power for the listeningprocess. When the UE has received the random access response message,the information included in the random access response message isindividually processed. If the random access procedure is acontention-based procedure, an uplink transmission 2.4 including a UEidentifier is sent to the eNodeB. If the random access procedure is anon contention-based procedure, the process may end after step 2.3.Before receiving 2.5 the contention resolution message (MSG4) from theeNodeB, the UE actively listens for this message during a time perioddefined by a contention resolution timer. According to an embodiment,this invention is directed to decreasing power consumption during atleast one of the response window and the contention resolution timerwindow.

According to the current 3GPP standard, a UE can be configured with DRXmode for saving power consumption. Although there is no suggestion touse DRX mode in a random access procedure. Also, the DRX can only beconfigured by RRC signaling, i.e. an RRC connection has to be set upbefore DRX can be applied. Therefore, during an initial random accessprocedure where no RRC connection exists, DRX cannot be applied. Also,the current LTE standard defines the intervals of Response Window Sizeand Contention Resolution Timer as an active time period, i.e. always-onmonitoring is required. Thus, even if a random access procedure isinitialized due to e.g. an out-of sync state in RRC-Connected mode, DRXin a random access procedure cannot be applied.

To reduce power consumption at a random access procedure according to anembodiment of the invention, a DRX scheme is exchanged between the UEand the eNodeB during the random access procedure such that a messagetransmitted during the random access procedure may be transmitted to theUE according to the exchanged DRX scheme. The message transmittedaccording to the exchanged DRX scheme may be a random access responsemessage (MSG2) and/or a contention resolution message (MSG4). Accordingto an embodiment, the DRX scheme is exchanged by the eNodeB instructingthe UE of the selected DRX scheme to use. According to anotherembodiment, the DRX scheme is exchanged by the UE selecting DRX schemeby selecting a preamble which has a predefined relationship to a certainDRX scheme, and sending the preamble to the eNodeB.

A signaling diagram describing signaling between a UE 110 and an eNodeB120 during a random access procedure according to an embodiment is shownin FIG. 3. In this embodiment, a DRX scheme is selected by the UE forthe reception of at least a contention resolution message. The signalingstarts by the UE selecting 3.1 a random access preamble. Since there isa predefined mapping relationship between the random access preamblesand different DRX schemes, the UE when selecting a preamble also selectsa DRX scheme to be used for later transmission in DRX mode from theeNodeB to the UE. The selected DRX scheme defines e.g. the timeintervals of active/inactive periods for the UE and time offset of thestarting point for DRX transmission/reception. The UE transmits 3.2 thepreamble to the eNodeB. Since the eNodeB knows the mapping between thepreambles and the DRX scheme, the eNodeB would be informed of theselected DRX scheme when receiving the preamble.

The eNodeB then sends 3.3 a random access response (MSG2) to the UE. Theinformation in the random access response may include a Time advancecommand, UL grant and a temporary Cell Radio Network Temporary Identityvalue (C-RNTI). If the UE and the eNodeB have been set in DRX modeaccording to the DRX scheme of the preamble, the MSG2 may be sentaccording to the DRX mode. In this case, the UE is in DRX mode duringthe response window when the MSG2 may be received, and only wakes up tolisten to possible MSG2s at the active periods defined by the DRXscheme.

Thereafter, the UE sends 3.4 the UE identifier to the eNodeB in anuplink transmission (MSG3). As soon as the MSG3 is sent, the UE listensto a contention resolution message (MSG4) according to the selected DRXscheme. The eNodeB then responds 3.5 to the MSG3 with the MSG4. The MSG4is sent in an active period as defined by the DRX scheme. The randomaccess procedure succeeds after successful reception of MSG4. If notsucceeded, the random access procedure and the DRX mode according to theselected DRX scheme is stopped in order to retry to access again.

The step of predefining a mapping relationship between the random accesspreambles and the DRX schemes may either be hardcoded, e.g. defined in afuture specification, or broadcasted by the eNodeB beforehand, e.g. assystem information. By predefining a mapping relationship between thepreambles and the DRX schemes, no extra signaling is needed for UE ULtransmission, i.e. there is no impact on coverage performance. Themapping may be defined for different values of response window sizeand/or contention resolution timer such that correct DRX scheme may beselected adapted to a certain response window size and/or contentionresolution timer.

For the UE to select different DRX schemes, e.g. different DRX cyclesand time offsets, different information could be taken into account,such as UL traffic Quality of Service information and UE power status.

According to an alternative embodiment, the eNodeB may control the usageof DRX scheme even in this UE controlled embodiment. In this case, theeNodeB sends an instruction to the UE to use the selected DRX scheme oranother DRX scheme. This instruction may be sent in the random accessresponse message. In case the eNodeB sends an instruction to use anotherDRX scheme, the UE is reset to the instructed DRX scheme.

In another UE controlled method, the UE may send information on DRXusing the MSG3. Although, in that case extra information needs to besent compared to the MSG3 of today. Also, then it is only possible touse DRX mode for MSG4 and not MSG2.

In the description, the eNodeB is said to be set in DRX mode using theselected DRX scheme for DL transmissions. Strictly speaking, thetransmitter of the eNodeB is set in discontinuous transmission (TRX)mode with a TRX scheme that is in line with the selected DRX scheme.Although, to simplify, the eNodeB is said to be in DRX mode using thesame DRX scheme as the receiver of the UE.

FIG. 4 is a signaling diagram describing signaling between a UE and aneNodeB during a random access procedure according to another embodiment.In this embodiment, the eNodeB controls DRX scheme to be used. Thesignaling starts by the UE 110 selecting 4.1 a random access preambleand sending 4.2 the preamble to the eNodeB 120. The UE then activelylistens for the Random Access Response (MSG2) during the responsewindow. Before sending the MSG2, the eNodeB selects a DRX scheme to beused for communication in DRX mode between the eNodeB and the UE duringthe rest of the random access procedure. When deciding on which DRXscheme to select, the eNodeB may take into account e.g. UE prioritylevel and/or system load status. Also, DRX scheme may be selected basedon a value of the Contention resolution timer.

The eNodeB thereafter sends 4.3 the MSG2 to the UE. The MSG2 includesinformation on the selected DRX scheme. The MSG2 may also includeinformation such as time advance command, UL grant and temporary C-RNTI.The UE and the eNodeB are then set in DRX mode according to the selectedDRX scheme. Thereafter, the UE sends an uplink transmission includingthe UE identity. As soon as the MSG3 is sent, the UE wakes up and listento a contention resolution message (MSG4) according to the selected DRXscheme. The eNodeB then responds 3.5 to the MSG3 with the MSG4. The MSG4is sent in an active period as defined by the DRX scheme. The randomaccess procedure succeeds after successful reception of MSG4. If notsucceeded, the random access procedure, and the DRX mode according tothe selected DRX pattern is stopped in order to retry to access again.

In an alternative embodiment, information of the selected DRX scheme canbe sent from the eNodeB to the UE in an implicit way. For example, apredefined rule can be employed as a mapping between a UL grant resourcelocation or a temporary C-RNTI value and the selected DRX pattern. Inthis way, it is also possible for a legacy UE to decode the informationin MSG2, even though a legacy UE will not use DRX mode, and at the sametime more advanced UEs can apply the DRX scheme information for powersaving.

In embodiments for implicitly sending information of the selected DRXscheme, already existing information, such as a UL grant resourcelocation or a temporary C-RNTI value, in the random access responsemessage is used. Then the temporary C-RNTI or the UL grant resourcelocation value is an indicator of the selected DRX scheme. Some kind ofmapping may be used to connect a certain existing information value witha certain DRX pattern. In alternatives when the information of theselected DRX scheme is sent explicitly it may be sent as new informationbits in the random access response message.

According to an alternative embodiment, a DRX cycle can be aligned withan MSG3 retransmission period, i.e. the UE is only awake according tothe DRX scheme, when MSG3 want to retransmit, in which case it would beawake anyway. Thereby, further UE battery power is saved.

FIG. 5 describes an exemplary embodiment of a method in a mobileterminal 110 for communication with a base station 120 in a wirelessnetwork during a random access procedure. The method comprisesexchanging 202, during the random access procedure, information on aselected DRX scheme to be used for communication between the mobileterminal and the base station in the random access procedure, setting204 the mobile terminal in DRX mode according to the selected DRX schemeand receiving 206 at least one message from the base station during therandom access procedure, wherein the at least one message wastransmitted according to the selected DRX scheme.

FIG. 6 describes another embodiment of a method in a mobile terminal forcommunication with a base station in a wireless network during a randomaccess procedure. The method may start by in the mobile terminalpredefining 212 a mapping relationship between preambles in a group ofpreambles and DRX schemes in a group of DRX schemes such that each DRXscheme is mapped to at least one preamble. The predefinition may behardcoded or received in a message from the base station. Thereafter,information on the selected DRX scheme is exchanged between the mobileterminal and the base station by the mobile terminal selecting 214 DRXscheme out of the group of DRX schemes by selecting a preamble out ofthe group of preambles, which selected preamble is mapped to theselected DRX scheme. Then the selected preamble is transmitted 216 tothe base station. The mapping between the selected preamble and theselected DRX scheme is known to the mobile terminal and the basestation. Since the mapping is known also to the base station the basestation can map the received preamble to the selected DRX scheme, andthe base station can be set in DRX mode according to the selected DRXscheme. Further, the mobile terminal is set 204 in DRX mode according tothe selected DRX scheme. Thereafter, a random access response messagemay be received 222 according to the selected DRX scheme. This meansthat the random access response message may be transmitted from the basestation at time intervals defined by the DRX scheme, which timeintervals are in line with the time intervals when the mobile terminalwakes up to listen to messages from the base station. Thereafter, amobile terminal identifier may be transmitted 224 to the base station,followed by receiving 226 a contention resolution message from the basestation, which contention resolution message may be transmittedaccording to the selected DRX scheme.

According to an embodiment, the mobile terminal selects 214 the DRXscheme based on UL traffic Quality of Service and/or mobile terminalpower status. According to another embodiment, the mobile terminal mayreceive an instruction to use the selected DRX scheme or another DRXscheme from the base station in the random access response message(MSG2). In this embodiment the base station may control the finalselection of DRX scheme even though the DRX scheme was originallyselected by the mobile terminal. If this embodiment is used, the basestation and the mobile terminal will not be set in DRX mode until afterreceiving this instruction in MSG2. As a result, only MSG4 and not MSG2can be sent according to the selected DRX scheme.

FIG. 7 describes yet another embodiment of a method in a mobile terminalfor communication with a base station in a wireless network during arandom access procedure. The method comprises receiving 232 informationon a selected DRX scheme from the base station, setting 234 the mobileterminal in DRX mode according to the selected DRX scheme and receiving236 a contention resolution message from the base station, whichcontention resolution message was transmitted from the base stationaccording to the selected DRX scheme. The step of receiving 232information on a selected DRX scheme from the base station may be seenas an example of the step of exchanging 202 information on a selectedDRX scheme to be used for communication between the mobile terminal andthe base station in the random access procedure, in which example theselection of DRX scheme is controlled by the base station. Theinformation on the selected DRX scheme may be received 232 from the basestation in a random access response message.

According to an embodiment, in which the base station controls theselection of DRX scheme, the mobile terminal receives 232 theinformation on the selected DRX scheme by receiving an indication fromthe base station to use a preamble that is mapped to the selected DRXscheme. The mapping is known to the mobile terminal and the basestation. This embodiment is directed to a non-contention based selectionof preamble. Since the mobile terminal is instructed to select apreamble mapped to a selected DRX scheme, which mapping is known both tothe mobile terminal and the base station, both the mobile terminal andthe base station will know which DRX scheme to use.

FIG. 8 describes an embodiment of a method in a base station forcommunication with a mobile terminal in a wireless network during arandom access procedure. The method comprises exchanging 302, during therandom access procedure, information on a selected DRX scheme to be usedfor communication between the mobile terminal and the base station inthe random access procedure, setting 304 the base station in a DRX modeaccording to the selected DRX scheme, and transmitting 306 at least onemessage to the mobile terminal during the random access procedure,wherein the at least one message is transmitted according to theselected DRX scheme.

FIG. 9 describes another embodiment of a method in a base station forcommunication with a mobile terminal in a wireless network during arandom access procedure. The method starts by the base station selecting312 DRX scheme. The DRX scheme may be selected based on at least one ofa mobile terminal priority level and a network load status.Alternatively, the DRX scheme may be selected to synchronize with HybridAutomatic Repeat Request, HARQ, feedback. Further, information on theselected DRX scheme is exchanged between the mobile terminal and thebase station by the base station transmitting 314 the information on theselected DRX scheme to the mobile terminal. The method may also comprisesetting 304 the base station in DRX mode according to the selected DRXscheme and transmitting 306 a message to the mobile terminal accordingto the selected DRX scheme. In an embodiment, the information on theselected DRX scheme is transmitted 314 in a random access responsemessage.

FIG. 10 describes yet another embodiment of a method in a base stationfor communication with a mobile terminal in a wireless network during arandom access procedure. The method may start by in the base stationpredefining 322 a mapping relationship between preambles in a group ofpreambles and DRX schemes in a group of DRX schemes such that each DRXscheme is mapped to at least one preamble. The predefinition may behardcoded or received in a message from the network. Thereafter,information on the selected DRX scheme is exchanged between the mobileterminal and the base station by the base station receiving 324 apreamble from the mobile terminal, which preamble is mapped to theselected DRX scheme, wherein the mapping between the preamble and theselected DRX scheme is known to the mobile terminal and the basestation. The method may further comprise setting 304 the base station ina DRX mode according to the DRX scheme mapped to the received preamble,and transmitting 330 a random access response message to the mobileterminal. The random access response message may be transmittedaccording to the selected DRX scheme. Alternatively, the method furthercomprises transmitting an instruction to use the selected DRX schemeaccording to the preamble, or another DRX scheme to the mobile terminalin the random access response message. In that case, the random accessresponse message may not be transmitted according to the selected DRXscheme. Further, the method may comprise receiving 332 a mobile terminalidentifier from the mobile terminal, and transmitting 334 a contentionresolution message to the mobile terminal, which contention resolutionmessage is transmitted according to the selected DRX scheme.

FIG. 11 describes a mobile terminal 110 and a base station 120 formutual communication in a wireless network during a random accessprocedure. According to an embodiment, the mobile terminal is arrangedfor exchanging, during the random access procedure, with the basestation 120, information on a selected DRX scheme to be used forcommunication between the mobile terminal and the base station in therandom access procedure. Further, the mobile terminal 110 comprises asetting unit 113 for setting the mobile terminal in DRX mode accordingto the selected DRX scheme, and a receiver 116 for receiving at leastone message from the base station during the random access procedure,wherein the at least one message was transmitted according to theselected DRX scheme. The setting unit 113 may be arranged in a processor112.

According to an embodiment, for exchanging information on a selected DRXscheme with the base station during the random access procedure, thereceiver 116 of the mobile terminal is arranged to receive theinformation on the selected DRX scheme from the base station. Theinformation on the selected DRX scheme may be received in a randomaccess response message. The information on the selected DRX scheme maybe used by the setting unit when setting the mobile terminal in DRX modeaccording to the selected DRX scheme. The information on the selectedDRX scheme may be stored in the database 115.

According to an embodiment, for exchanging information on a selected DRXscheme with the base station during the random access procedure, themobile terminal has a selection unit 114 and a transmitter 118. Theselection unit 114 is arranged for selecting DRX scheme out of a groupof DRX schemes by selecting a preamble out of a group of preambles,which selected preamble is mapped to the selected DRX scheme. Theselection unit 114 may be arranged in the processor 112. The transmitter118 is arranged for transmitting the selected preamble to the basestation, wherein the mapping between the selected preamble and theselected DRX scheme is known to the mobile terminal and the basestation. When the selecting unit 114 selects the preamble it may fetch apreamble in a database 115 of the mobile terminal. Also, a mappingrelationship is predefined between each of the preambles in the databaseand each of the DRX schemes such that each DRX scheme is mapped to atleast one preamble. The mapping relationship between the preambles andthe DRX schemes may be received from the base station or hardcoded inthe mobile terminal. The mapping relationship may be stored in thedatabase where it is accessible for the selection unit. Also theselected DRX scheme may be stored in the database 115 or in a memory inthe processor 112.

According to an embodiment, the base station 120 is arranged forexchanging, during the random access procedure, with the mobileterminal, information on a selected DRX scheme to be used forcommunication between the mobile terminal and the base station in therandom access procedure. The base station comprises a setting unit 123for setting the base station in a DRX mode according to the selected DRXscheme, and a transmitter 128 for transmitting at least one message tothe mobile terminal during the random access procedure, wherein the atleast one message is transmitted according to the selected DRX scheme.The setting unit 123 may be arranged in a processor 122. The informationon the selected DRX scheme may be used by the setting unit when settingthe base station in DRX mode according to the selected DRX scheme. Theinformation on the selected DRX scheme may be stored in a database 125.

According to an embodiment, for exchanging information on a selected DRXscheme with the mobile terminal during the random access procedure, thetransmitter 128 of the base station 120 is arranged to transmit theinformation on the selected DRX scheme to the mobile terminal. Thetransmitter 128 may be arranged for transmitting the information on theselected DRX scheme in a random access response message. The basestation may further comprise a selection unit 124 for selecting DRXscheme. The selection of DRX scheme may be based on at least one of amobile terminal priority level and a network load status. The selectionunit 124 may be arranged in the processor 122. The selection unit 114may be arranged for selecting DRX scheme out of a group of DRX schemes,which group of DRX schemes may be stored in the database 125 or in aninternal memory of the processor 122.

According to another embodiment, for exchanging information on aselected DRX scheme with the mobile terminal during the random accessprocedure, the base station 120 has a receiver 126 arranged to exchangethe information on the selected DRX scheme by receiving a preamble fromthe mobile terminal 110, which preamble is mapped to the selected DRXscheme. The mapping between the preamble and the selected DRX scheme isknown to the mobile terminal and the base station. Further, a mappingrelationship is predefined between each of a group of preambles and eachof a group of DRX schemes such that each DRX scheme is mapped to atleast one preamble. The mapping relationship between the preambles andthe DRX schemes may be received from the network or may be hardcoded inthe base station. The mapping relationship may be stored in the database125 where it is accessible for the processor 122. When receiving apreamble, the processor checks the mapping in e.g. the database andinterprets that the received preamble is mapped to the selected DRXscheme. Also the selected DRX scheme may be stored in the database 125or in an internal memory of the processor 122.

Further, the transmitter 128 may be arranged for transmitting, duringthe random access procedure, a random access response message and/or acontention resolution message to the mobile terminal according to theselected DRX scheme.

Although, the invention is described in terms of a 3GPP LTE-basedsystem, it is not limited to such a system. It might as well be used forexample for a HSPA based system, a W-CDMA based system etc.

The terms base station/eNodeB, and mobile terminal/user equipment areused in an interchangeable manner throughout this disclosure.

While the solution has been described with reference to specificexemplary embodiments, the description is generally only intended toillustrate the inventive concept and should not be taken as limiting thescope of the solution. The solution is defined by the appended claims.

The invention claimed is:
 1. A method in a mobile terminal forcommunication with a base station in a wireless network during a randomaccess procedure, the method comprising: exchanging, during the randomaccess procedure between the mobile terminal and the base station,information on a selected discontinuous reception (DRX), scheme to beused for communication between the mobile terminal and the base stationin the random access procedure, wherein exchanging information on theselected DRX comprises sending a random access preamble, out of aplurality of preambles, that is mapped to the selected DRX scheme;setting the mobile terminal in DRX mode according to the selected DRXscheme; and receiving at least one message from the base station duringthe random access procedure, wherein the at least one message wastransmitted according to the selected DRX scheme.
 2. Method according toclaim 1, wherein the information on the selected DRX scheme is exchangedby the mobile terminal receiving the information on the selected DRXscheme from the base station.
 3. Method according to claim 2, whereinthe information on the selected DRX scheme is received from the basestation in a random access response message.
 4. Method according toclaim 2, wherein the mobile terminal receives the information on theselected DRX scheme by receiving an indication from the base station touse a preamble that is mapped to the selected DRX scheme, and whereinthe mapping is known to the mobile terminal and the base station. 5.Method according to claim 1, wherein exchanging the information on theselected DRX scheme by the mobile terminal comprises: selecting a DRXscheme out of a group of DRX schemes by selecting the random accesspreamble out of a group of preambles, and transmitting the selectedrandom access preamble to the base station, wherein the mapping betweenthe selected random access preamble and the selected DRX scheme is knownto the mobile terminal and the base station.
 6. Method according toclaim 5, wherein receiving at least one message from the base stationduring the random access procedure comprises receiving a random accessresponse message from the base station according to the selected DRXscheme.
 7. Method according to claim 5, wherein the mobile terminalselects the DRX scheme based on UL traffic Quality of Service and/ormobile terminal power status.
 8. Method according to claim 5, furthercomprising receiving an instruction to use the selected DRX scheme oranother DRX scheme from the base station in a random access responsemessage.
 9. Method according to claim 5, further comprising predefininga mapping relationship between each of the preambles in the group ofpreambles and each of the DRX schemes in the group of DRX schemes suchthat each DRX scheme is mapped to at least one preamble.
 10. Methodaccording to claim 1, further comprising: transmitting a mobile terminalidentifier to the base station, and receiving a contention resolutionmessage from the base station, which contention resolution message wastransmitted according to the exchanged DRX scheme.
 11. A method in abase station for communication with a mobile terminal in a wirelessnetwork during a random access procedure, the method comprising:exchanging, during the random access procedure between the mobileterminal and the base station, information on a selected discontinuousreception (DRX), scheme to be used for communication between the mobileterminal and the base station in the random access procedure, whereinexchanging information on the selected DRX comprises receiving a randomaccess preamble, out of a plurality of preambles, that is mapped to theselected DRX scheme; setting the base station in a DRX mode according tothe selected DRX scheme; and transmitting at least one message to themobile terminal during the random access procedure, wherein the at leastone message is transmitted according to the selected DRX scheme. 12.Method according to claim 11, wherein information on the selected DRXscheme is exchanged by transmitting the information on the selected DRXscheme to the mobile terminal.
 13. Method according to claim 12, whereinthe information on the selected DRX scheme is transmitted in a randomaccess response message.
 14. Method according to claim 11, furthercomprising: selecting DRX scheme based on at least one of a mobileterminal priority level and a network load status.
 15. Method accordingto claim 11, wherein exchanging the information on the selected DRXscheme by the base station comprises: receiving the random accesspreamble from the mobile terminal, wherein the mapping between therandom access preamble and the selected DRX scheme is known to themobile terminal and the base station.
 16. Method according to claim 15,wherein transmitting at least one message to the mobile terminal duringthe random access procedure comprises transmitting a random accessresponse message from the base station according to the selected DRXscheme.
 17. Method according to claim 15, further comprisingtransmitting an instruction to use the selected DRX scheme according tothe preamble, or another DRX scheme to the mobile terminal in a randomaccess response message.
 18. Method according to claim 11, furthercomprising: receiving a mobile terminal identifier from the mobileterminal, and transmitting a contention resolution message to the mobileterminal, which contention resolution message is transmitted accordingto the selected DRX scheme.
 19. A mobile terminal for communication witha base station in a wireless network during a random access procedure,comprising: a setting unit for setting the mobile terminal in adiscontinuous reception (DRX) mode according to a selected DRX scheme;and a receiver for receiving at least one message from the base stationduring the random access procedure, wherein the at least one message wastransmitted according to the selected DRX schemes and wherein: themobile terminal is configured to exchange information on the selectedDRX scheme to be used for communication between the mobile terminal andthe base station during a random access procedure with the base station;and the mobile terminal configured to exchange information on theselected DRX scheme comprises the mobile terminal configured to send arandom access preamble, selected from a plurality of preambles, that ismapped to the selected DRX scheme.
 20. Base station for communicationwith a mobile terminal in a wireless network during a random accessprocedure, comprising: a setting unit for setting the base station in adiscontinuous reception (DRX) mode according to a selected DRX scheme;and a transmitter for transmitting at least one message to the mobileterminal during the random access procedure, wherein the at least onemessage is transmitted according to the selected DRX scheme, andwherein: the base station is configured to exchange information on theselected DRX scheme to be used for communication between the mobileterminal and the base station during a random access procedure with themobile terminal; and the base station configured to exchange informationon the selected DRX scheme comprises the base station configured toreceive a random access preamble, selected from a plurality ofpreambles, that is mapped to the selected DRX scheme.